Bring a large pot of salted water to a boil. Add the pasta, and cook for 1 minute less than the time recommended on the box. Drain.
Meanwhile make the pesto. In a food processor, add the walnuts and garlic and puree. Add the basil, lemon juice, salt, and pepper, and run the food processor, gradually streaming in the olive oil until the pesto is thoroughly pureed. Add the Parmesan and puree for another 30 seconds. Set aside.
In a separate skillet heated over medium high heat, add 2 tablespoons of olive oil. Season the shrimp with salt, pepper, and chili powder. Sear the shrimp until golden and just cooked through. Do not overcook your shrimp! Remove the shrimp from the pan and set aside.
To the pan, add the cream, pesto and salt and pepper to taste. Cook for about 1 minute, until thickened slightly. Stir in the pasta and continue cooking for another minute. Serve, with the shrimp on top.